1. Field of the Invention
The present invention relates to a channel switching valve for use in liquid chromatographs and the like.
2. Description of the Related Art
High-performance liquid chromatographs have a flow channel, through which liquid flows under high pressure, and require channel switching.
For such a purpose, a channel switching valve is conventionally used. A conventional channel switching valve includes a stator to be connected to flow channels and a rotor, and is configured to perform channel switching by rotating the rotor in a state where the stator and the rotor are in contact with each other at their surfaces (see Japanese Unexamined Patent Publication No. 1-307575).
In such a channel switching valve, the contact surface of the stator has ports to be connected to flow channels and the contact surface of the rotor has a switching groove for interconnecting two of the ports of the contact surface of the stator. The stator is interposed between a housing top, to which flow channels are to be connected, and the rotor. The stator may be separately formed from the housing top or formed integrally therewith. The rotor is attached to the distal end of a rotary shaft, and is pressed against the stator by an elastic member, such as a spring, with a force required to allow the switching groove to be liquid-tight. That is, the rotor and the stator are in contact with each other at their surfaces, thereby preventing liquid leakage from the switching groove. The rotor is rotated by receiving a rotational driving force from the rotary shaft. In order to perform channel switching, the connection between the ports of the stator is changed by rotating the rotor.
In the case of such a conventional channel switching valve, the rotor is made of a soft material, such as resin, and the stator is made of a material harder than that of the rotor, such as stainless steel. Therefore, the contact surface of the rotor is worn out due to the prolonged use of the channel switching valve. This may cause an increase in the rotational torque of the channel switching valve, fluid leakage, and cross-contamination by liquid remaining in the worn-out contact surface of the rotor.
Further, as described above, the rotor is pressed against the stator by a given force to prevent liquid leakage. Therefore, in a case where the rotor is made of resin, the contact surface of the rotor is scraped off and scrapings are generated by friction caused by the rotation of the rotor. In this case, the scrapings from the rotor also flow into a column connected downstream from the channel switching valve, which becomes the cause of deterioration of the column.
On the other hand, the rotor may be made of a hard material such as ceramics. In this case, unlike the rotor made of resin, scrapings are not generated, but it is necessary to reduce surface roughness of contact surfaces of both the stator and the rotor and to achieve high flatness of these contact surfaces to maintain sealing. However, if such contact surfaces are pressed against each other by a great force, a so-called “linking” phenomenon in which mirror-polished surfaces adhere to each other occurs, which interferes with the rotation of the rotor.
In order to maintain liquid-tightness achieved by the rotor and the stator, the rotor is often made of resin. In this case, however, there is a problem that the rotor always pressed against the stator by a great force is significantly worn out by its rotation, which leads to a shorter life expectancy of the valve.
In a case where a channel switching valve needs to be liquid-tight under conditions where liquid flows under high pressure, a rotor needs to be pressed against a stator by a great force. However, in some cases, for example, when liquid is allowed to flow under low pressure, such a great pressing force is not required depending on the intended purpose. Despite this, in the case of conventional channel switching valves, the pressing force of a rotor against a stator is constant and cannot be changed.